The present invention relates to a control valve for a variable capacity compressor to be employed in air conditioners for vehicles, etc., and in particular to a control valve for a variable capacity compressor, which is designed to supply, upon requirements, a coolant gas from a discharge pressure region to a crankcase.
A variable capacity compressor provided with a cylinder, a piston, a wobble plate, etc. has been conventionally employed for compressing and discharging a coolant gas of an air conditioner for vehicles, etc. One example of this conventional variable capacity compressor is constructed such that it comprises a coolant gas passage for communicating a discharge pressure region with a crankcase, so that the quantity of coolant gas to be discharged can be changed in conformity with changes in inclination angle of the wobble plate which can be effected through an adjustment of the pressure inside the crankcase. The adjustment of pressure inside the crankcase is performed by feeding a high pressure compressed coolant gas from the discharge pressure region to the crankcase while adjusting the opening degree of a control valve disposed at an intermediate portion of the coolant gas passage.
FIGS. 6 and 7 show one example of such a control valve 100' for a variable capacity compressor (hereinafter referred to simply as a control valve) (see Japanese Patent Unexamined Publication (Kokai) H/9-268,974). This control valve 100' is disposed neighboring on the rear housing 210 of the variable capacity compressor 200 and is designed to adjust the pressure inside the crankcase 231 which is disposed in a front housing 230 and next to the a cylinder block 220 of the variable capacity compressor 200.
In the interior of the crankcase 231, there are housed a wobble plate 240 which is mounted on a driving shaft 250 in such a manner that it can slide along the axial direction of the driving shaft 250 and can incline about the driving shaft 250, and also a guide pin 241 of the wobble plate 240, which is made slidable along a supporting arm 252 of a rotatable supporting body 251. The wobble plate 240 is connected via a couple of shoes 242 with a piston 260 which is slidably disposed in a cylinder bore 221.
The wobble plate 240 is designed to swing in the directions indicated by the arrows so as to change its inclination angle in conformity with a difference in pressure between a suction pressure Ps inside the cylinder bore 221 and a pressure Pc inside the crankcase 231. The stroke width of the forward and backward movement of the piston 260 in the cylinder bore 221 can be determined based on this inclination angle. Further, the inclinatory movement in the direction of arrows of the wobble plate 240 causes a cutoff body 270 contacting with a middle portion of the wobble plate 240 to move forward or backward in a housing bore 222.
The rear housing 210 is provided with suction chambers 211a and 211b each constituting an inlet pressure region, and with discharging chambers 212a and 212b each constituting a discharge pressure region. When the piston 260 is moved forward and backward as a result of the inclinatory movement of the wobble plate 240, the coolant gas in the suction chamber 211a is sucked into the cylinder bore 221 from a suction port 213 and then compressed to a predetermined pressure before it is discharged through a discharge port 214 into the discharging chamber 212a.
An inlet passage 215 formed at the central portion of the rear housing 210 is communicated with the housing bore 222 and also with the suction chamber 211b through a through-hole 216. When the wobble plate 240 is moved toward the cutoff body 270, the cutoff body 270 is caused to move toward the inlet passage 215 thereby causing the through-hole 216 to be closed ultimately by the cutoff body 270.
Between the inlet passage 215 and the upper end portion of the control valve 100', there is formed a pressure-checking passage 217 for introducing the suction pressure Ps into the control valve 100'. The discharging chamber 212b is communicated with the crankcase 231 via gas inlet passages 218 and 219 of the control valve 100'. These gas inlet passages 218 and 219 are designed to be opened or closed by means of a valve member 106' of the control valve 100'. In this case, it is designed such that a discharging pressure Pd inside the discharging chamber 212b is allowed to be introduced via the gas inlet passage 218 to a valve chamber port 113', while the pressure Pc inside the crankcase 231 is allowed to be introduced via the gas inlet passage 219 to a valve chamber port 114'. Further, it is also designed such that the suction pressure Ps is allowed to be introduced via the pressure-checking passage 217 into a sucking pressure-introducing port 115'.
If a temperature detected by an indoor sensor 281 is higher than a set temperature of a temperature-setting device 282 at the moment when an actuating switch 280 of air conditioner is turned on, a controlling computer 283 outputs a command to magnetize the solenoid 101' of the control valve 100'. As a result, an electric current is fed via an actuating circuit 284 to the solenoid 101' thereby causing the solenoid 101' to generate a suction force, due to which a movable core 102' is attracted, against the urging force (biasing force) of a spring 103', toward a fixed core 104'.
As the movable core 102' is moved in this manner, the valve member 106' attached to a solenoid rod 105' is caused to move, against the urging force of a forced opening spring 107', in the direction to decrease the opening degree of a valve hole 108'. As a result of this movement of the valve member 106', a pressure-sensitive rod 109' formed integral with the valve member 106' is moved upward thereby pushing up bellows 111' which is detachably connected with the pressure-sensitive rod 109' through a pressure-sensitive rod receiver 110'.
At this moment, the displacement of bellows 111' is caused in conformity with changes of the suction pressure Ps to be introduced via the pressure-sensitive passage 217 into the interior of the pressure-sensitive chamber 112', thereby giving a load to the pressure-sensitive rod 109'. Thus, the control valve 100' is designed such that the opening degree of the valve hole 108' by means of the valve member 106' is determined by a balance among the suction force of the solenoid 101', the urging force by the bellows 111' and the urging force by the forced opening spring 107'.
If the cooling load is large in this case for instance, i.e. if a difference between the temperature detected by the indoor sensor 281 and the set temperature of the room temperature-setting device 282 is large, the suction force between the movable core 102' and the fixed core 104' is increased whereby increasing the force of the valve member 106' to bias the valve hole 108' in the direction to decrease the opening degree thereof, thus making it possible to perform the opening and closing of the valve member 106' with the lower suction pressure Ps.
When the opening degree of valve by means of the valve member 106' is decreased, the quantity of coolant gas to be fed to the crankcase 231 from the discharging chamber 212b via the gas inlet passages 218 and 219 is decreased, thus lowering the crankcase pressure Pc in the interior of the crankcase 231.
Further, if the cooling load is large, the suction pressure Ps inside the cylinder bore 221 is increased whereby generating a difference in pressure between the suction pressure Ps inside the cylinder bore 221 and the crankcase pressure Pc inside the crankcase 231, thus enlarging the inclination angle of the wobble plate 240, whereby causing the cutoff body 270 to keep away from the inlet passage 215 to open the passage 216.
In the aforementioned conventional control valve 100', it is designed such that the discharge pressure Pd is introduced via the gas inlet passage 218 into the valve chamber port 113' of the control valve 100' as shown in FIG. 7. Since the discharge pressure Pd is high and the coolant gas generating such the high discharge pressure Pd releases an intense heat as it is compressed up to a predetermined pressure by the forward and backward movement of the piston 260, the control valve 100' itself is heated to high temperatures by the intense heat released from the coolant gas.
When the control valve 100' itself is heated to high temperatures in this manner, the temperature of the solenoid 101' is also risen so that the suction force of the movable core 102' which is originating from the solenoid 101' is weakened, thereby raising a problem that the opening or closing accuracy of the valve hole 108' by means of the valve member 106' is deteriorated. Furthermore, in the case of the conventional control valve 100', the bellows 111' is required to be incorporated into the pressure sensitive chamber 112' with the interior of the pressure sensitive chamber 112' being maintained in a closed state. Therefore, there is no space for introducing an adjusting jig into the pressure sensitive chamber 112' from outside, thereby making it impossible to perform the adjustment of loading force of the bellows 111'.
Additionally, since the application point of suction from the solenoid 101' to the solenoid rod 105' is kept away from the application point of the urging force by the bellows 111', not only there is a possibility that the solenoid rod 105' may be rattled as it is moved at the occasion of closing the valve, but also the valve member 106' may possibly be non-uniformly contacted with the valve hole 108' due to the aforementioned rattling of the solenoid rod 105' because the distal end portion of the valve member 106' for closing the valve hole 108' is simply made flat, and hence the opening or closing accuracy of the valve is hindered from being improved.